Control system for HF alkylation

ABSTRACT

A control system for regulating the reaction zone temperature in a process for the acid-catalyzed alkylation of an isoparaffin with an olefinic feed stream containing mixed olefins. The reaction zone temperature is adjusted to obtain the optimum for a given feed composition, in order to maximize the octane rating of the ultimate normally liquid alkylate product. The control system effects rapid compensation for continuing changes in feed composition which, at a fixed reaction zone temperature, otherwise adversely affect the octane rating.

APPLICABILITY OF INVENTION

The control system herein described is intended for utilization in aprocess for the production of a normally liquid alkylate product via thereaction of an isoparaffin with an olefin. Although intended for use inany acid-catalyzed alkylation process -- e.g. sulfuric acid alkylation-- my invention is most applicable to those processes effected with ahydrogen fluoride catalyst. For more than a quarter of a century, thedemand for high octane fuels, possessing enhanced anti-knockcharacteristics, has increased at a staggering rate. These improvedfuels are required in voluminous quantities to satisfy, theever-accelerating degree of consumption. Various processes have beendeveloped which have proved successful in alleviating the intertwinedproblems attendant supply, quality and demand. Among the first of suchprocesses was the acid-catalyzed alkylation of an isoparaffin with anolefin, both generally normally vaporous, to produce a higher molecularweight, normally liquid isoparaffin. Since isoparaffins, in contrast tonormal paraffins, possess significantly higher octane ratings, and thusimprove anti-knock properties, processes capable of efficientlyeffecting the alkylation reaction have gained wide acceptance within thepetroleum industry.

For many economic and technical reasons, the alkylation processcatalyzed by hydrogen fluoride catalyst appears to be preferred. HFalkylation of an isoparaffin with an olefin has, since the adventthereof, experienced a multitude of changes and improvements withrespect to unit design and/or operating techniques. The control systemencompassed by my inventive concept constitutes an improvement whichaffords enhancement of operational stability, while simultaneouslyproviding economic advantages. Although applicable to the alkylation ofan olefinic hydrocarbon having from about three to about seven carbonatoms per molecule, with an isoparaffin having from about four to aboutseven carbon atoms per molecule, the present control system is uniquelyadvantageous in those processes where isobutane is alkylated with anolefinic feed stream containing at least two olefins selected from thegroup consisting of propylene, 1-butene, 2-butene and isobutylene.Therefore, in the interest of brevity, further description of thepresent control system will be directed toward the HF-catalyzedalkylation of isobutane with mixed olefins having three or four carbonatoms per molecule. Many processes integrated into a single petroleumrefining operation result in product streams containing significantquantities of lower molecular weight olefinic hydrocarbons. Principalamong such processes is the well known fluid catalytic cracking process;others include thermal cracking, or pyrolysis units, coking operationsand visbreaking. The olefinic feed streams are generally recovered byway of gas concentration facilities which are specifically intended toconcentrate the C₃ - and C₄ -olefins. Exemplary of such mixed olefinconcentrates, recovered from one or more of the indicated processes, isone containing about 51.3% by volume propylene, 48.2% by volume of mixedbutylenes and about 0.5% by volume of mixed amylenes.

Investigations have indicated that the quality of the liquid alkylateproduct is, at a given reaction zone pressure, dependent upon thetemperature at which the reaction mixture is maintained. Since theacid-catalyzed alkylation process is exothermic, temperature control ofthe reaction mixture, via indirect heat exchange with a suitable coolingmedium, has been, and continues to be a commonly practiced technique.This relatively simple temperature control system will suffice where thefeed stream is a substantially pure olefinic hydrocarbon. However, thefeed stream in virtually 100% of the acid-catalyzed alkylation processesconstitutes a mixture of two or more of the aforementioned olefinichydrocarbons. This contributes a significant degree of complexity withrespect to temperature control of the reaction mixture. Considering, forthe sake of illustration, substantially pure olefinic feed streams, thequality of the alkylate produced from 1-butene is improved through anincrease in the reaction temperature, while that produced from either2-butene, or isobutylene is improved by a decrease in the reactiontemperature. Additionally, a higher quality alkylate product is producedfrom a propylene feed stream at higher temperatures than those which areoptimum for the alkylation of C₄ -olefins. Since the character of theolefinic feed stream is dependent to a large extent upon the operationof other units within the overall refinery, which units are subject totheir own peculiar operating parameters, the composition of the olefinicfeed stream introduced into the alkylation system is constantlychanging.

One popular prior art alkylation technique entails recycling a portionof the reaction zone effluent, after removal therefrom of the greaterproportion of hydrogen fluoride, to the reaction zone. The principaladvantage resides in a reduction in overall utility cost for the entireunit. Initially, the total reaction mixture is introduced into the lowervessel of a stacked, two-vessel system. The lower vessel serves as amixing, or soaking zone, after which the effluent is charged to theupper vessel which functions as an acid settler. There is provided anacid phase, as a bottoms stream, substantially free from the majorportion of hydrocarbon, and an upper hydrocarbon phase free from themajor portion of HF. An aliquot portion of the latter, having ahydrocarbon/HF mol ratio of about 20.0:1.0 to about 50.0:1.0, isrecycled to the reaction zone, generally in admixture with the olefinicfeed stream. The amount so recycled is most often in the range of about20.0 to about 100.0%, based upon the original feed stream. Thehydrocarbon portion of the recycled stream is a mixture of alkylateproduct, unreacted isobutane and butanes. As such, it introduces anadded factor which must be considered with respect to temperaturecontrol of the reaction mixture within the reaction zone. The presentcontrol system additionally compensates for the effect brought about bychanges in the composition and temperature of this recycled effluentstream.

The control system of the present invention affords a method foreffecting the rapid compensation of feed stream composition changes withrespect to the quality of the normally liquid alkylate product. There isafforded an enhancement of the steady-state operation of the system,particularly with respect to the stability of alkylate product quality,as well as the economic advantages attendant an increase in operationalefficiency.

OBJECTS AND EMBODIMENTS

A principal object of the present invention is to afford an improvementin the hydrogen fluoride-catalyzed alkylation of olefinic hydrocarbons.A corollary objective is to enhance the character of steady-stateoperation attendant the alkylation of a normally vaporous isoparaffinwith a normally vaporous olefinic hyrocarbon to produce a normallyliquid alkylate product.

A specific object of my invention involves the control of reaction zonetemperature when alkylating an isoparaffin with a mixed olefinic feedstream while simultaneously recycling a portion of the alkylate producteffluent to the reaction zone.

Therefore, one embodiment of my invention provides a control system foruse in a process for alkylating an isoparaffin with an olefinic feedstream, to produce a normally liquid alkylate product, wherein (1) saidfeed stream contains at least two olefinic hydrocarbons and is contactedin admixture with a hydrogen fluoride catalyst, in a reaction zone, and(2) at least a portion of the reaction zone effluent is recycledthereto, which control system regulates the temperature within saidreaction vessel, and comprises, in cooperative combination: (a) conduitmeans for introducing a cooling medium into said reaction zone, and forremoving it therefrom, said cooling medium indirectly contacting thereaction mixture within said zone; (b) first flow-varying means foradjusting the flow of said cooling medium into said reaction zone; (c)second flow-varying means for adjusting the flow of effluent recycled tosaid reaction zone; (d) a hydrocarbon analyzer receiving a sample ofsaid normally liquid alkylate product and developing an output signalrepresentative of a composition characteristic of said sample; (e) firstsignal-receiving means to which said output signal is transmitted bysaid hydrocarbon analyzer, said first signal-receiving means in turntransmitting said signal to said first flow-varying means, whereby theflow of said cooling medium is adjusted in response to said compositioncharacteristic; and, (f) second signal-receiving means to which saidoutput signal is transmitted by said hydrocarbon analyzer, said secondsignal-receiving means in turn transmitting said signal to said secondflow-varying means, whereby the flow of said recycled effluent isadjusted in response to said composition characteristic.

In another embodiment, my inventive concept encompasses a process foralkylating an isoparaffin with an olefinic feed stream, containing atleast two olefins, which process comprises the steps of: (a) reactingsaid isoparaffin with said feed stream, in admixture with a hydrogenfluoride catalyst, in an alkylation reaction zone, at alkylatingconditions resulting in a reaction product effluent containing normallyliquid alkylate; (b) regulating the temperature of the reaction mixture,within said reaction zone, through indirect contact therein with acooling medium, the flow of which is adjusted by first flow-varyingmeans; (c) recycling at least a portion of the reaction zone effluent tosaid reaction zone, the flow of which is adjusted by second flow-varyingmeans; (d) recovering said normally liquid alkylate from said producteffluent; (e) introducing a sample of said alkylate into a hydrocarbonanalyzer and developing therein an output signal which is representativeof a composition characteristic of said sample; and, (f) transmittingsaid output signal to comparator means which compares the rate of changeand actual value of said composition characteristic, generates a secondoutput signal and transmits said second output signal to at least one oftwo signal-receiving means, the first of which transmits said signal tosaid first flow-varying means, whereby the flow of cooling medium isadjusted, and the second of which transmits said signal to said secondflow-varying whereby the flow of said recycled effluent is adjusted, inresponse to said composition characteristic.

Other objects and embodiments will become apparent from the followingadditional description of the present inventive concept and the controlsystem encompassed thereby. In other such embodiments, the hydrocarbonanalyzer comprises a stabilized cool flame generator having aservo-positioned flame front, and the output signal generated thereby isrepresentative of the octane number of the alkylate product sample.

PRIOR ART

Candor compels recognition and acknowledgment that the prior art isreplete with a wide variety of publications, inclusive of issuedpatents, which are directed toward the acid-catalyzed alkylation of anisoparaffin with an olefin. This is particularly true with respect tohydrogen fluoride alkylation which traces its development over anapproximate 30-year period. No attempt will be made herein toexhaustively delineate the hydrogen fluoride alkylation art; however, itis believed that a brief description of several innovations, for thepurpose of illustrating the applicability of the present improvement,will serve to define the areas to which the present technique isapplicable.

U.S. Pat. No. 3,560,587 (Cl. 260-683.48) describes the hydrogen fluoridealkylation of an isoparaffin/olefin mixture in a system whichincorporates a reaction cooler, reaction soaker and a hydrogen fluorideacid-settler. U.S. Pat. No. 3,686,354 (Cl. 260-683.43) is fairlyillustrative of a complete hydrogen fluoride alkylation processincluding reaction vessels, reaction effluent separation for acidrecovery, and product separation for the recovery of the normally liquidalkylate. In this particular system, the alkylate product is separatedinto a relatively high-octane fraction and a relatively low-octanefraction, the latter being further treated with additional isoparaffinand hydrogen fluoride catalyst.

The present control system is intended for utilization in HF-catalyzedalkylation processes of the type above illustrated. The integration andutilization of control systems in a petroleum refining process isconsidered to be among recent technological innovations. In thisrespect, the published literature is slowly developing its own field ofart, some of which includes issued patents. For example, U.S. Pat. No.3,759,820 (Cl. 268-64) discloses the systematized control of amulti-reaction zone process in response to two different qualitycharacteristics of the ultimately desired product. U.S. Pat. No.3,649,202 (Cl. 23-253A) involves the control of reaction zone severityin response to the octane rating of the normally liquid producteffluent, and is primarily directed toward the well known catalyticreforming process. Other examples of the systematized control ofpetroleum refining processes are found in U.S. Pat. No. 3,751,229 (Cl.23-253A), U.S. Pat. No. 3,748,448 (Cl. 235-151.12) and U.S. Pat. No.3,756,921 (Cl. 196-132).

As hereinbefore stated, the present control system is utilized toalleviate the problems attendant reaction zone temperature control in anacid-catalyzed alkylation process wherein an isoparaffin is alkylatedwith a mixed olefinic feed stream and a portion of the reaction zoneeffluent is recycled thereto. These difficulties, principally arisingout of the utilization of an olefinic feed stream containing propylene,1-butene, 2-butene and isobutylene do not appear to be recognized eitherin the appropriate alkylation art, or in the control system literature.

SUMMARY OF THE INVENTION

As hereinbefore set forth, my invention is directed toward animprovement in the control of reaction zone temperature while alkylatingan isoparaffin/olefin reactant stream. Although applicable to thealkylation of isobutane with a butylene-containing feed stream, theprocess is also adaptable for utilization of other isoparaffinic andolefinic feed stocks. Suitable isoparaffinic hydrocarbons are thosehaving from about four to about seven carbon atoms per molecule,including isobutane, isopentane, neopentane, one or more of theisohexanes and various branched-chain heptanes. Similarly, the olefinicreactant stream contains from about three to about seven carbon atomsper molecule, and is inclusive of propylene, 1-butene, 2-butene,isobutylene, the isomeric amylenes, hexenes and various heptenes.

The alkylation reaction mixture comprises hydrogen on fluoride catalyst,an isoparaffin and a mixed olefinic feed stream. With respect to thelatter, the feed stream generally contains at least two olefinichydrocarbons selected from the group consisting of propylene, 1-butene,2-butene and isobutylene. Hydrogen fluoride catalyst is utilized in anamount sufficient to provide a catalyst/hydrocarbon volume ratio, withinthe reaction zone, of from about 0.5 to about 3.0. As a generalpractice, commercial anhydrous hydrogen fluoride will be charged to thealkylation system as the catalyst. It is possible to use hydrogenfluoride which contains as much as about 10.0% water; however, excessivedilution should be avoided since it tends to reduce the alkylatingactivity of the catalyst while introducing severe corrosion problemsinto the system. In order to reduce the tendency of the olefinic portionof the hydrocarbon feed stock to undergo polymerization prior toalkylation, the molar proportion of the isoparaffin to olefinichydrocarbons is maintained at a value greater than about 1.0:1.0, up toabout 20.0:1.0, and preferably from about 3.0:1.0 to about 15.0:1.0.

Alkylation reaction conditions include temperatures in the range ofabout 0° to about 200°F., and preferably from about 30° to about 110°F.In view of the fact that the alkylation reactions are highly exothermic,suitable means for removing heat from the reaction zone is required. Ingeneral practice, the reaction zone is designed such that it functionsas an indirect heat-exchanger. A cooling medium is introduced into thereaction zone and contacts the reaction mixture therein. Generally, thequantity of cooling medium introduced is controlled by direct responseto the internal temperature of the reaction mixture. While such a basictechnique admittedly offers some form of temperature control, it isclearly susceptible to a relatively large cycling range. In effect, thistechnique maintains the reaction zone temperature above a predeterminedminimum and below a predetermined maximum, the latter to avoidadditional polymerization reactions which adversely affect the productquality.

Alkylation pressures are suffficiently high to maintain the hydrocarbonfeed stream and hydrogen fluoride catalyst in substantially liquidphase; that is, pressures from about 15 psig. to about 600 psig. Thecontact time in the alkylation reaction zone is conveniently expressedin terms of a space-time relationship which is defined as the volume ofcatalyst within the reaction zone divided by the volume rate per minuteof hydrogen reactants charged to the zone. Usually, the space-timerelationship will be less than about 5 minutes and preferably less thanabout 2 minutes. The product effluent from the alkylation reaction zoneis introduced into a separation zone generally comprising a two-vesselstacked system. The mixture is initially introduced into the lowervessel which serves as a vertical mixer, or soaking zone. The mixer issized and designed to provide an average residence time in the range ofabout 60 to about 1200 seconds. After the desired residence time, theeffluent is introduced into the upper vessel which serves as a settlerto provide a hydrocarbon stream substantially free from the majorportion of hydrogen fluoride, and a settled hydrogen fluoride phasesubstantially free from the major proportion of hydrocarbons. Inaccordance with a relatively recent technique, at least a portion of thereaction zone effluent (the hydrocarbon stream) is emulsified andrecycled to the alkylation reaction zone, in an amount of from 20.0 toabout 100.0%, based upon the original feed stream plus recycle. Thesettled hydrogen fluoride is recycled to the reaction zone in admixturewith regenerated hydrogen fluoride. The reaction zone effluent generallycontains a minor proportion of polymer products nothwithstandingtemperature control of the reaction mixture. In order to prevent thebuild-up of polymer products within the system, a relatively minorproportion of the settled hydrogen fluoride phase is introduced into anacid regenerator. Hydrogen fluoride recovered therefrom is recycled tothe alkylation reaction zone.

That portion of the hydrocarbon phase separated in the settler vesseland not recycled to the reaction zone, is introduced into an isostripperfractionating column for the recovery of the normally liquid alkylateproduct. Propane, unreacted isobutane and a minor quantity of hydrogenfluoride catalyst are removed as an overhead stream and introduced intoa separate settling zone, from which the hydrogen fluoride is recycledto the reaction zone. The hydrocarbon phase from this settler isintroduced into a depropanizng column, with isobutane being removed as abottoms fraction, recycled in part to the reaction zone and in part tothe acid-regenerator for the purpose of stripping hydrogen fluoride fromthe polymer products which are removed as a bottoms phase. A principallyvaporous phase, predominantly propane, and containing a minor quantityof hydrogen fluoride, is introduced into a hydrogen fluoride strippingcolumn. The hydrogen fluoride is removed as an overhead fraction andintroduced into the isostripper settler for ultimate return to thereaction zone. Propane is removed from the bottom of the hydrogenfluoride stripper and sent to storage; this stream is generallysubjected to both alumina treating and potassium hydroxide treating toremove trace quantities of hydrogen fluoride. Similarly, although thenormally liquid alkylate product is generally recovered substantiallyfree from hydrogen fluoride, cautious operating techniques dictate thatthe same be subjected to similar treatments.

The foregoing is representative of a typical hydrogen fluoridealkylation process. As previously stated, the present control system isintended for integration into such a unit for the purpose of achieving agreater degree of efficiency with respect to reaction zone temperaturecontrol, accompanied by an enhancement of the steady-state operation ofthe entire system. As previously stated, the character of the olefinicfeed stream to an HF alkylation unit is generally dependent upon theoperation of other processes within the refinery. Since these otherprocesses are subjected to their own peculiar operating parameters, thecomposition of the olefinic feed stream is constantly changing. Thiscontributes a particular problem with respect to temperature control ofthe alkylation reaction zone mixture. Considering only propylene,1-butene, 2-butene and isobutylene, the normally liquid alkylate productquality is improved by increasing the reaction temperature, with respectto 1-butene, and by decreasing the temperature of the reaction mixturewith respect to 2-butene and isobutylene. This anomaly is furthercompounded by virtue of the fact that a higher quality alkylate productresults from a propylene feed stream processed at higher temperturesthan those which are considered optimum for the alkylation of C₄-olefins.

As hereinbefore stated, a portion of the hydrocarbon phase recovered asan overhead stream from the settler, is recycled to the reaction zone.Although the hydrocarbon portion of this recycle stream is constantlychanging, in view of the changes in the original olefinic feed stream tothe unit, the hydrocarbon/HF mol ratio thereof will generally be in therange of about 20.0:1.0 to about 50.0:1.0. Recycling this mixture ofalkylate product, unreacted isobutane and butanes introduces an addedfactor to be considered with respect to temperature control of thereaction mixture within the reaction zone. Through the use of thepresent control system, there is afforded additional compensation forthe effect brought about by changes in the composition and temperatureof this recycled effluent stream.

In accordance with the present invention, a hydrocarbon analyzer isemployed to receive a sample of the normally liquid alkylate productremoved as a bottoms stream from the isostripping column. An outputsignal, which is representative of a composition characteristic of thesample, is developed by the hyrocarbon analyzer. This output signal istransmitted to signal-receiving means, or controller means, the latterin turn transmitting the signal to flow-varying means whereby the flowof the cooling medium into the alkylation reaction zone is adjusted andthe flow of recycled reaction zone effluent is adjusted, both inresponse to the varying composition characteristic. In a preferredembodiment, the output signal is initially transmitted to comparatormeans which compares the rate of change and actual value of saidcomposition characteristic, generates a second output signal andtransmits said second signal to at least one of the controller means, inorder to regulate either the flow of cooling medium, or the flow ofrecycled effluent, or both. Complete details of the hydrocarbonanalyzer, intended for utilization as an essential element of thepresent control system may be obtained upon reference to U.S. Pat. No.3,463,613 (Cl. 23-230).

As stated therein, a composition characteristic of a hydrocarbon samplecan be determined by burning the same in a combustion tube underconditions generating a stabilized cool flame. The position of the flamefront is automatically detected and employed to develop a signal which,in turn, is utilized to vary a combustion parameter such as combustionpressure, induction zone temperature or air flow, in a manner whichimmobilizes the flame front regardless of changes in the compositioncharacteristic of the hydrocarbon sample. The change in the combustionparameter, required to immobilize the flame front following a change ofsample composition, is, therefore, corollatable with the compositioncharacteristic change. An appropriate read-out device, of the type wellknown in the appropriate art, connecting with the hydrocarbon analyzer,may be calibrated in terms of the desired identifying characteristic as,for example, the octane rating.

The hydrocarbon analyzer is characterized as comprising a stabilizedcool flame generator having a servo-positioned flame front. The type ofanalysis affected thereby is not a compound-by-compound analysis such asthat presented by instruments including mass spectrometers andvapor-phase chromatographs. On the contrary, the analysis is representedby a continuous output signal which is responsive to and indicative ofhydrocarbon composition and, more specifically, is corollatable with oneor more conventional identifications or specifications of petroleumproducts including Reid vapor pressure, ASTM or Engler distillations,or, for motor fuels, anti-knock characteristics such as research octanenumber, motor octane number, or a composite thereof.

The hydrocarbon analyser receives a hydrocarbon sample (preferablycontinuously) containing predominately gasoline boiling rangecomponents; the output signal provides a direct measure of octanenumber. For brevity, the hydrocarbon analyzer is herein referred to as"an octane monitor".

The control system will further include comparator means which initiallyreceives the output signal from the hydrocarbon analyzer, and comparesthe rate of change and actual value of the composition characteristicwith previously received values. A second output signal is generated andtransmitted to the signal-receiving means, or flow controllers, to resetthe set points thereof in response to successive comparisons of thecomposition characteristic. The flow control means in turn transmit thesignal to the flow-varying means, whereby the flow of the cooling mediumand the flow of the effluent recycle stream is adjusted in responsethereto. Where desired, second comparator means can be included forcomparing the actual value of the composition characteristic withpreviously determined deviation limits and for generating an adjustmentoutput signal in response to this comparison. When the value lies beyondthe set limits, and the rate of change with respect to time indicatesthat the value will continue to depart from such limits, the secondcomparator means will generate an adjustment signal to alter the rate ofchange. Details of comparator means, as utilized in a control system fora reaction process, may be found in U.S. Pat. No. 3,748,448 (Cl.235-151.12).

In further describing my invention, reference will be made to theaccompanying drawing which is presented for the sole purose ofillustrating a typical prior art HF alkylation process having integratedtherein the control system of the present invention. In the drawing, theprocess is presented by way of a simplified flow diagram in whichdetails such as pumps, instrumentation and other controls, quenchsystems, heat-exchange and heat-recovery circuits, valving, start-uplines and similar hardware have been eliminated as non-essential to anunderstanding of the techniques involved. The use of such miscellaneousappurtenances, to modify the process as illustrated, will be evident tothose possessing the requisite skill in the art of petroleum refiningtechnology.

DESCRIPTION OF DRAWING

The drawing will be described in conjunction with a commercially-scaledunit designed for the alkylation of isobutane with a mixed olefin feedstream, containing propylene, various butylenes and amylenes, in anexchanger-type reaction vessel. The olefinic charge stream, in theamount of about 5,482 Bbl./day, enters the process via line 1; make-upisobutane is introduced via line 3; and, field butane, in the amount of923 Bbl./day is introduced into the system via line 20, theisobutane-rich portion thereof being recycled by way of line 2 tocombine with the olefinic hydrocarbon and make-up isobutane mixture inline 1. Also introduced into the reactant mixture is a portion of thereaction zone effluent (8,316.66 mol/hr.) via line 42, the source ofwhich is hereinafter described. That this recycle stream is shown asbeing combined with the olefinic feed stream in line 1 is not essentialto the present invention; that is, it could be shown as initiallycombining with the make-up isobutane being introduced via line 3. In anyevent, the entire reactant mixture continues through line 1, beingintroduced thereby into reactor 4. From thee fresh feed charge streams,it is desired to produce a full boiling range, normally liquid alkylateproduct having a Reid vapor pressure of about 10.0 lbs. and a clearoctane rating of about 93.0.

With specific reference now to the drawing, 5,482 Bbl./day of theolefinic feed stream (884.45 mols/hr.), is introduced into the processthrough line 1, and is admixed with 49,878 Bb1./day (7,107.45 mols/hr.)of an isobutane rich recycle stream in line 2, containing 107.16 mols ofHF acid; 2,452 Bbl./day (347.65 mols/hr.) of make-up isobutane (95.0% byvolume) is introduced via line 3 and 8,316.66 mols/hr. of recycledeffluent via line 42, containing 212.78 mols/hr. of HF acid. The mixturecontinues through line 1 into alkylation reactor 4 which is designed tofunction as a heat-exchanger having multiple feed injection points,which technique is well known and not, therefore, illustrated herein.Hydrogen fluoride, in an amount of 88,360 Bb1./day (54,255.23 mols/hr.),is recycled from settler 13 into reactor 4 by way of line 5. This streamis inclusive of 169.95 mols/hr. of regenerated acid from line 6, alsocontaining 297.31 mols/hr. of an isobutane-rich stream and 107.16mols/hr. of settled HF acid recovered in line 7 as hereinafterdescribed. In reactor 4, the isobutane/olefinic hydrocarbon mol ratio isabout 13.0:1.0 and the HF acid/hydrocarbon volumetric ratio is about1.48:1.0, exclusive of the recycle stream in line 42. Reactor 4 ismaintained at a pressure of about 233 psig., with the HF acid andreactant stream being introduced at a temperature of about 100°F. Thematerial balance around reaction zone 4, exclusive of the HF acidstream, is presented in the following Table I, with the concentrationsof the various components being given in terms of mols/hr. forconvenience.

                  TABLE I                                                         ______________________________________                                        Reaction Zone Material Balance                                                Component       Charge       Effluent                                         ______________________________________                                        Ethane          0.92         0.92                                             Propylene       271.49       --                                               Propane         583.58       599.71                                           Butylenes       256.25       --                                               Isobutane       6896.52      6352.38                                          N-Butane        505.62       510.36                                           Amylenes        2.76         --                                               Isopentane      80.45        98.88                                            N-Pentane       0.59         --                                               Hexane-plus     37.85        541.63                                           Polymer Products                                                                              --           0.17                                             ______________________________________                                    

As hereinbefore set forth, HF alkylation of an isoparaffin/olefinreactant mixture is highly exothermic, and must be tempered through theuse of a cooling medium. In the illustration, the exothermic heat ofreaction is removed through the use of 8,017 gallons per minute of water(about 85°F.) entering via line 9, and exiting via line 8 at atemperature of about 90°F. The total reaction product effluent iswithdrawn through line 10 at a temperature of about 100°F. and apressure of about 218 psig.

The product effluent continues through line 10 into mixer/soaker 11wherein it is maintained for an effective residence time of about 8minutes. After this holding period, the product effluent is transferredvia line 12 into HF acid settler 13. Settled HF acid is removed via line14 in the amount of 88,013 Bb1./day (54.040.62 mols/hr.), at a pressureof about 203 psig. Of this amount, 87,735 Bb1/day (53,870.77 mols/hr.)are diverted through line 5 as acid recycle to reactor 4. Generally, theremaining 278 Bb1/day (169.95 mols/hr.) is accumulated until asufficient quantity is available for introduction via line 14 into acidregenerator 15. Regenerator 15 functions at a bottom pressure of about155 psig., a bottom temperature of about 350°F., a top pressure of about145 psig. and a top temperature of about 160°F. HF acid is stripped frompolymer products by the introduction, via line 16, of an isobutane-richstream (212.22 mols/hr.), at a temperature of 450°F. and a pressure ofabout 160 psig. Polymer products, in the amount of about 3.2 Bb1./day(0.17 mols/hr.) are recovered through line 17, at a pressure of about155 psig. and a temperature of about 350°F. A portion of theisobutane-rich stream from line 16 is diverted through line 32 in theamount of about 85,09 mols/hr., cooled to a temperature of about 100°F.,and introduced as reflux into acid regenerator 15. The overhead streamin line 6, comprising 297.31 mols/hr. of hydrocarbons and 169.95mols/hr. of regenerated HF acid, is recycled to combine with the settledacid in line 5, and returned to reactor 4. The material balance withrespect to acid regenerator 15 is presented in the following Table II:

                  TABLE II                                                        ______________________________________                                        Acid Regenerator Material Balance                                             Component                                                                              Line Number                                                                 14     32      16       6      17                                      ______________________________________                                        Propane  --       1.00    6.46   7.46   --                                    Isobutane                                                                              --       78.66   198.82 277.48 --                                    N-Butane --       4.91    6.45   11.36  --                                    Isopentane                                                                             --       0.52    0.48   0.99   --                                    HF Acid  169.95   --      --     169.95 --                                    Polymers 0.17     --      --     --     0.17                                  ______________________________________                                    

The hydrocarbon-rich phase from settler 13, at a temperature of about100°F. and a pressure of about 203 psig., is withdrawn through line 18in an amount of 16,633.32 mols/hr., of which 425.56 mols/hr. is HF acid.About 50.0% of this hydrocarbon-rich phase is diverted via line 42 to becombined with the olefinic feed stream in line 1. The remainder,consisting of 8,103.88 mols/hr. of hydrocarbons and 212.78 mols/hr. ofHF acid, is heated to a temperature of about 170°F. and introduced intoisostripper 19 at a pressure of about 152 psig. Field butane, at atemperature of about 100°F., enters the upper section of isostripper 19through line 20, in an amount of 133.07 mols/hr. A normal butane-richstream, in the amount of 89.16 mols/hr., is recovered as a side-cut vialine 21, and is subjected to treatment with potassium hydroxide for theremoval of trace quantities of HF acid. Isostripper 19 functions at abottom temperature of about 371°F., a bottom pressure of about 160psig., a top temperature of about 140°F. and a top pressure of about 152psig. The normally liquid alkylate product is recovered through line 22in an amount of about 5,932 Bbl./day (579.97 mols/hr.), and is alsosubjected to caustic treating for acid removal. An isobutane-richstream, in the amount of 6,897.43 mols/hr., including 19.42 mols/hr. ofa pump flush stream (not illustrated) from depropanizer 27, is recycledvia lines 2 and 1 to reactor 4. Also recovered in line 2 is HF acid inthe amount of 107.16 mols/hr. Overhead vapors, consisting of 1,380.08mols/hr. of hydrocarbons and 120.85 mols/hr. of HF acid, is withdrawnthrough line 23.

Of this amount, 690.04 mols/hr. of hydrocarbons and 13.69 mols/hr. of HFare utilized as reflux to isostripper 19; the composition of thehydrocarbon phase is about 0.91 mols of ethane, 166.55 mols of propane,495.23 mols of isobutane, 24.92 mols of N-butane and 2.44 mols ofisopentane. The component composition of the various charge and effluentstreams, exclusive of HF acid, are presented in the following Tables IIIand IV:

A portion of the overhead from line 23 is diverted as reflux to the topof isostripper 19; this portion consists of 690.04 mols/hr. ofhydrocarbons and 13.69 mols/hr. of HF. The remainder is admixed with14.05 mols/hr. of HF from line 24, and is introduced into settler 25.Settled acid, in the amount of 107.16 mols/hr., is recycled to reactor 4by way of line 7 and 5. Hydrocarbons, in the amount of 703.11 mols/hr.,and HF acid, in the amount of 14.05 mols/hr., are introduced via line 26into depropanizer 27. A propane concentrate, containing 14.05 mols/hr.of HF acid is recovered as an overhead stream in line 28 beingintroduced thereby into HF stripper 29.

                  TABLE III                                                       ______________________________________                                        Isostripper Feed Streams                                                      Component   Line 18        Line 20                                            ______________________________________                                        Ethane      0.92           --                                                 Propylene   --             --                                                 Propane     599.71         3.10                                               Butylenes   --             --                                                 Isobutane   6352.38        62.63                                              N-Butane    590.72         64.99                                              Isopentane  98.88          1.52                                               N-Pentane   --             0.83                                               Hexane-plus 541.63         --                                                 ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                        Isostripper Effluent Streams                                                  Component                                                                              Line 23   Line 2     Line 21 Line 22                                 ______________________________________                                        Ethane   1.83      --         --      --                                      Propylene                                                                              --        --         --      --                                      Propane  336.11    412.71     --      --                                      Butylenes                                                                              --        --         --      --                                      Isobutane                                                                              987.75    5935.17    4.30    1.17                                    N-Butane 49.54     418.35     83.28   50.23                                   Isopentane                                                                             4.84      72.59      1.52    24.01                                   N-Pentane                                                                              --        --         --      0.69                                    Hexane-plus                                                                            --        37.85      0.06    503.72                                  ______________________________________                                    

The bottoms stream, in an amount of 540.03 mols/hr., is withdrawnthrough line 30 and utilized as follows: 32.74 mols/hr. are employed asa pump flush stream (not illustrated); 297.31 mols/hr. are divertedthrough line 16 for use in acid regenerator 15; and, 210.02 mols/hr.continue through line 30 for recycle to reactor 4 via line 2.Depropanizer 27 functions with a bottom pressure of about 315 psig., abottom temperature of about 220°F., a top temperature of about 140°F.and a top pressure of about 305 psig. The material balance fordepropanizer 27 is presented in the following Table V:

                  TABLE V                                                         ______________________________________                                        Depropanizer Material Balance                                                 Component                                                                              Line 26     Line 28     Line 30                                      ______________________________________                                        Ethane   0.92        0.92        --                                           Propane  169.72      159.40      10.31                                        Isobutane                                                                              504.63      2.74        501.88                                       N-Butane 25.38       --          25.38                                        Isopentane                                                                             2.48        --          2.48                                         ______________________________________                                    

Hydrogen fluoride, in an amount of about 14.05 mols/hr. is withdrawn asan overhead stream in line 24, and admixed with the isostripper overheadin line 23. The 163.07 mols/hr. of hydrocarbons are recovered via line31. HF stripper 29 functions with a top temperature of about 140°F., anda pressure of about 310 psig. and a bottoms temperature of 150°F., and apressure of about 320 psig.

The normally liquid alkylate product, withdrawn via line 22 has a ReidVapor Pressure of about 9.9 lbs., a clear octane rating of about 93.3(research method), 104.2 with 3.0 cc. of tetraethyl lead, and a gravityof 74.6 °API. The results of a 100 ml. ASTM distillation are presentedin the following Table VI:

                  TABLE VI                                                        ______________________________________                                        Alkylate Product ASTM Distillation                                            Volume Percent   °F.                                                   ______________________________________                                        Initial Boiling Point       92                                                 5.0%                  119                                                    10.0%                  136                                                    20.0%                  170                                                    30.0%                  196                                                    40.0%                  206                                                    50.0%                  212                                                    60.0%                  218                                                    70.0%                  223                                                    80.0%                  234                                                    90.0%                  273                                                    95.0%                  --                                                     End Boiling Point          356                                                ______________________________________                                    

Octane monitor 33 is field-installed adjacent isostripper 19; itutilizes a stabilized cool flame generator having a servo-positionedflame front. The flow of oxidizer (air) and fuel (alkylate producteffluent from line 22) are fixed, as is the induction zone temperature.Combustion pressure is the parameter which is varied in such manner thatthe stabilized cool flame front is immobilized.

Upon experiencing and detecting a change in a compositioncharacteristic, in this illustration octane number, the change inpressure required to immobilize the flame front within octane monitor 33provides a direct indication of the change in the sample delivered tothe analyzer's combustion chamber by way of line 34. Typical operatingconditions for the octane monitor are: air flow, 3,500 cc./min. (STP);fuel flow, 1.0 cc./min.; induction zone temperature, Research Octane,700°F.; induction zone temperature, Motor Octane, 800°F.; combustionpressure, 4.0 to 20.0 psig.; and, octane range (max.), 80 to 102. Theactual calibrated span of the octane monitor as herein employed, willgenerally be narrower. For example, where the target octane rating is95.0 Clear (Research Method), a suitable span may be 90-96 researchoctane. When such a relatively narrow span is employed, the octanenumber change is essentially directly proportional to the change incombustion pressure. As shown in the drawing, the sample system maycomprise a sample loop taking, for example, liquid at a rate of about100 cc./min. via line 34 and returning it by way of line 35, the sampleitself being injected, from an intermediate point, at a controlled rateby a metering pump to the combustion tube of the octane monitor.

The octane monitor output signal is transmitted through line 36 toultimately reset the set point of controllers 39 and 44. The latter willthen make the appropriate adjustments, by way of lines 40 and 45, incontrol valves 41 and 46, either to decrease, or increase the flow ratesof the effluent recycle in line 42, and of the cooling medium in line 9.It is understood, of course, that control valve 46 can be installed inline 8, the cooling medium exit line from reaction zone 4. In apreferred technique, the octane monitor output signal is transmitted vialine 36 into comparator means 37, and therefrom through lines 38 and 43into controllers 39 and 44. Since the sample of alkylate product fromline 22 is taken continuously, and a varying output signal iscontinuously being transmitted via line 36, rapid compensation for thechanges in the olefinic composition of the feed stream in line 1 isafforded. Additionally, the effect of effluent recycle via line 42 isreadily offset. Comparator 37 is capable of functioning to change eitherthe flow of cooling medium through line 9, the flow of recycled effluentin line 42, or both. By checking the current output signal, received vialine 36, against the previous signal, comparator 37 transmits the propersignal or signals to controllers 39 and 44 to correct for any indicateddifference.

To illustrate further, it will be presumed that the olefinic feed streamcomposition changes to the extent that there is a decrease in thecontent of 1-butene, in which case the reaction zone temperature is toohigh, and an increase in the propylene content greater than the changein C₄ -olefins, in which case the temperature is too low. Octane monitor33 senses the decreasing octane rating of the alkylate product andtransmits a corresponding output signal through line 36 to comparator37. The latter compares and checks this current signal against theprevious signal and transmits output signals via lines 43 and 38 tocontrollers 44 and 39, in order to correct the difference and reset thecontrol points. The controllers in turn cause valves 46 and 41 to closesuch that the flow of cooling medium and effluent recycle is decreased,and the reaction zone temperature increased. When the ultimate effect issensed by octane monitor 33, comparator 37 will compare and check thethen current output signal, and make the appropriate change, or changesrequired to achieve the target octane number.

Through the utilization of the present control system, a refinerfunctioning with a mixed olefin feed stream, as the charge to an HFalkylation system, is afforded close control over either a desiredtarget octane rating, or over maximizing the octane rating, regardlessof the changes in feed composition.

I claim as my invention:
 1. For a process for alkylating an isoparaffinwith an olefinic feed stream, to produce a normally liquid alkylateproduct, wherein (1) said feed stream contains at least two olefinichydrocarbons and is contacted in admixture with a hydrogen fluoridecatalyst, in a reaction zone, and (2) at least a portion of the reactionzone effluent is recycled thereto, the control system, for regulatingthe temperature within said reaction zone, which comprises, incooperative combination:a. conduit means for introducing a coolingmedium into said reaction zone, and for removing it therefrom, saidcooling medium indirectly contacting the reaction mixture within saidzone; b. first flow-varying means for adjusting the flow of said coolingmedium into said reaction zone; c. second flow-varying means foradjusting the flow of effluent recycled to said reaction zone; d. ahydrocarbon analyzer receiving a sample of said normally liquid alkylateproduct and developing an output signal representative of a compositioncharacteristic of said sample; e. first signal-receiving means to whichsaid output signal is transmitted by said hydrocarbon analyzer, saidfirst signal-receiving means in turn transmitting said signal to saidfirst flow-varying means, whereby the flow of said cooling medium isadjusted in response to said composition characteristic; and, f. secondsignal-receiving means to which said output signal is transmitted bysaid hydrocarbon analyzer, said second signal-receiving means in turntransmitting said signal to said second flow-varying means, whereby theflow of said recycled effluent is adjusted in response to saidcomposition characteristic.
 2. The control system of claim 1 furthercharacterized in that said hydrocarbon analyzer comprises a stabilizedcool flame generator having a sevo-positioned flame front.
 3. Thecontrol system of claim 1 further characterized in that said outputsignal is transmitted to comparator means which compares the rate ofchange and actual value of said composition characteristic, generates asecond output signal and transmits said second signal to at least one ofsaid signal-receiving means.